32lm3400 dead no standby

[jonny78]

Hi guys! Set is completely dead! Checked the psu and a blue ceramic cap had exploded also the fuse was dead so I've replaced both of them with the correct value replacements but it's still dead nothing voltages from psu to mainboard are all 0! I haven't got a multimeter at the minute though ( cheap Chinese one fell apart so ordered a better one) does anyone know what are the main causes of a completely dead set are? I've read alot about lg sets with faulty mainboards! Cheers!

[jonny78]

Re: 32lm3400 dead no standby

psu is EAX64560501
mainboard is Eax64909901

[dick_barton]

Re: 32lm3400 dead no standby

Do you have any photo's of your boards and any voltage readings taken? ALl helpful.

[jonny78]

Re: 32lm3400 dead no standby

Hi sorry! please see attached photos! blue capacitor replaced is C102 ( you can see burn mark) and F101 (FUSE) also the readings are as follows:

N.C=0
12V=0
12V=0
12V=0
GND=0
GND=0
3.5V=0
3.5V=0
GND=0
GND=0
24V=0
PWR-ON=0

[budm]

Re: 32lm3400 dead no standby

You have two power supply sections:
1) The SMPS IC 501 is for the always on 3.5V standby power supply section.
2) That C102 is the snubber cap for the MOSFET Q101 which is for the switched power supply that will only come on when PWR-ON control signal is present.

Right you do not have Standby power to run the main board so that will be the section you need to test first.
What DCV do you have when measured right between the two legs of the main filter cap C110?

[jonny78]

You have two power supply sections:
1) The SMPS IC 501 is for the always on 3.5V standby power supply section.
2) That C102 is the snubber cap for the MOSFET Q101 which is for the switched power supply that will only come on when PWR-ON control signal is present.

Right you do not have Standby power to run the main board so that will be the section you need to test first.
What DCV do you have when measured right between the two legs of the main filter cap C110?

Hi thanks for the info! I've measured the main filter cap and the reading is 0!

[dick_barton]

Re: 32lm3400 dead no standby

Connect your meter set to AC volts and measure the voltage at the two black arrows "~". One meter lead on each point.
Then measure the DC voltage at the two red arrows. Red meter lead on "+" and black meter lead on "-".

Don't let the probes slip since this is the Live (HOT) side of the circuit board.

[jonny78]

Re: 32lm3400 dead no standby

thanks dick! sorry to sound like a noob but im not sure what you mean! with the tv plugged in and my meter set to DCV i measured the filter cap C110 red to positive black to negative and it reads as 0!

[dick_barton]

Re: 32lm3400 dead no standby

Connect your meter set to AC volts and measure the voltage at the two black arrows "~". One meter lead on each point.
Then measure the DC voltage at the two red arrows. Red meter lead on "+" and black meter lead on "-".

Don't let the probes slip since this is the Live (HOT) side of the circuit board.

Sorry left off the photo.

[budm]

Re: 32lm3400 dead no standby

Verify that the replacement fuse is good, also verify that you do have 230VAC between the two pins of the incoming AC connector on that power supply board.

[jonny78]

Re: 32lm3400 dead no standby

Sorry left off the photo.

cheers! measured both and both zero!

[jonny78]

Re: 32lm3400 dead no standby

Verify that the replacement fuse is good, also verify that you do have 230VAC between the two pins of the incoming AC connector on that power supply board.

check the fuse in circuit? whats the best way to test it? ive been testing it in diode mode..also measured the two pins and im getting 242VAC!

[jonny78]

Re: 32lm3400 dead no standby

https://www.youtube.com/watch?v=HuWly36NyEE <---- thats how i test fuses!

the fuse now appears to be bad if im testing it right lo but was 100% good before i soldered it in! and i know ive got the correct replacement 100%!

[dick_barton]

Re: 32lm3400 dead no standby

There appears to be some marks on the circuit board alongside C102 which I would check is not damaged. Also check the mosfet alongside it Q10x? is not short circuited.

[jonny78]

Re: 32lm3400 dead no standby

There appears to be some marks on the circuit board alongside C102 which I would check is not damaged. Also check the mosfet alongside it Q10x? is not short circuited.

hi ive already replaced c102 as it had blown.. will check the mosfet shortly! ive now only got 1 replacement fuse left though as they are fine but when i solder them in and turn the power on they seem to be blowing

[vinceroger69]

Re: 32lm3400 dead no standby

use a dim bulb tester saves blowing parts if it glows bright and stays bright when you power the psu on you still have a short circuit

have you tested the bridge rectifier?

[dick_barton]

Re: 32lm3400 dead no standby

hi ive already replaced c102 as it had blown.. will check the mosfet shortly! ive now only got 1 replacement fuse left though as they are fine but when i solder them in and turn the power on they seem to be blowing

Don't put the fuse in until you find what is causing it to blow.

You need to check the mosfet since the snubber capacitor was damaged and so is probably also damaged.

Hopefully you can find the fault. With the set disconnected from the mains and just using your multimeter set to ohms check the mosfet.

[jonny78]

Re: 32lm3400 dead no standby

hi thanks for the replies! you are right..the mosfet is shorted! ive uploaded the data sheet i cant find any of these in the uk only china and i cannot wait that long! would there be an equivalent one ?? many thanks!

[jonny78]

Re: 32lm3400 dead no standby

MDF10N65B is the fet in question!

[budm]

Re: 32lm3400 dead no standby

You need to verify that R114 is also OK or not, it should be <1 Ohm + your meter probes resistance.
Hopefully that IC101 is not damaged when that MOSFET shorted out otherwise you will damage your new MOSFET.